Mechanical Prosthesis versus Upsized Stented Bioprosthesis in Aortic Valve Replacement for Patients with a Small Aortic Annulus

Purpose: In patients with a small aortic annulus undergoing aortic valve replacement, surgeons sometimes choose to implant mechanical prostheses—which are associated with better hemodynamics than bioprostheses—rather than perform aortic annular enlargement. We aim to determine if choosing a mechanical valve is a viable alternative to performing aortic annular enlargement.

Methods: From January 2011 to March 2023, 295 patients with a native aortic annulus diameter of 23 mm or smaller underwent aortic valve replacement for aortic stenosis or aortic insufficiency with either a mechanical prosthesis without aortic annular enlargement (n=58) or an upsized stented bioprosthesis following aortic annular enlargement (n=237). Aortic annular enlargement was performed with either Nicks, Manouguian, or Y-incision procedures. The mechanical valve group was younger (51 years vs 66 years) and had a smaller body surface area (1.85 m2 vs 1.99 m2) than the upsized stented prosthesis group, but the proportion of males was similar [45% (24/58) vs 33% (78/237)]. Most comorbidities were similar between the groups, but the mechanical valve group had more dialysis [5.2% (3/58) vs 0%] and prior valve procedures [41% (24/58) vs 22% (53/237)], while the upsized bioprosthesis group had more diabetes [14% (8/58) vs 37% (88/237)] and hypertension [62% (36/58) vs 81% (193/237)].

Results: The mechanical valve group’s native aortic annulus diameter was larger (23 vs 21 mm), but prosthesis size was smaller (23 vs 25). Cross-clamp times were shorter in the mechanical valve group (120 vs 137 minutes), but cardiopulmonary bypass times were similar (156 vs 172 minutes). The mechanical valve group had more concomitant mitral/tricuspid valve procedures [36% (21/58) vs 11% (25/237)], but less coronary artery bypass grafting [12% (7/58) vs 23% (54/237)]. Perioperative outcomes including reoperation for bleeding, stroke, renal failure, heart block requiring pacemaker, prolonged ventilation, length of intensive care unit stay, and operative mortality [5.2% (3/58) vs 3.4% (8/237)] were similar between groups, but the mechanical valve group had less atrial fibrillation [10% (6/58) vs 33% (79/237)]. Kaplan-Meier estimation showed five-year survival was 78% (95% CI: 61%, 89%) in the mechanical valve group and 93% (95% CI: 88%, 96%) in the upsized bioprosthesis group (p=0.021) (Figure). On Cox proportional hazards regression, risk factors for late mortality included chronic lung disease, dialysis and mechanical valve (versus upsized bioprosthesis) with a hazard ratio of 2.95 (p=0.03) (Table). Five-year cumulative incidence of reoperation was 0% in the mechanical valve group and 7.9% in the upsized bioprosthesis group (p=0.048).

Conclusion: In patients with a small aortic annulus undergoing aortic valve replacement, annular enlargement to place an upsized bioprosthesis is safe and has better mid-term survival compared to using a mechanical valve without annular enlargement. We recommend annular enlargement over mechanical valve implantation in patients with an aortic annulus ≤23 mm.

Identify the source of the funding for this research project: NHLBI of NIH R01HL141891 and R01HL15177